Lithium secondary batteries, which are recently in the spotlight as a power source of portable and small electronic devices, may exhibit high discharge voltages that are two times or more than those of batteries using a typical alkaline aqueous solution by using an organic electrolyte solution. Thus, the lithium secondary batteries exhibit high energy density.
Graphite is mainly used as an anode material of the lithium secondary battery. However, graphite has a low capacity per unit mass of 372 mAh/g and a high-capacity lithium secondary battery may be difficult to be prepared by using graphite.
Anode active materials exhibiting higher capacity than graphite, i.e., materials electrochemically forming an alloy with lithium (lithium alloying material), such as silicon, tin, and an oxide thereof, exhibit a high capacity of about 1,000 mAh/g or more and a low charge and discharge potential of 0.3 V to 0.5 V, and thus, these materials are in the spot light as an anode active material for a lithium secondary battery.
However, volumes of these materials may expand because crystal structures thereof may be changed when electrochemically forming an alloy with lithium. In this case, since loss due to physical contact between active materials or active material and current collector of an electrode, which is prepared by coating with powder, occurs during charge and discharge, capacity of a lithium secondary battery may significantly decrease as charge and discharge cycles are repeated.
Also, in order to prevent volume expansion and improve lifetime characteristics when a silicon-based anode active material is used, research into the formation of pores on the surface and inside of the silicon-based anode active material has been conducted. However, there may be difficulty in having a desired performance of the battery by adjusting pore size, uniformity, and degree of porosity on the surface and inside of the silicon-based anode active material.
Thus, in order to increase the capacity of the lithium secondary battery, there is a need to develop a novel silicon-based material capable of effectively controlling the volume change. The novel silicon-based material allows the pore size, uniformity, and degree of porosity on the surface and inside of the silicon-based anode active material to be adjusted to satisfy capacity, efficiency, and cycle lifetime characteristics of the secondary battery, and thus, the novel silicon-based material may replace a typical anode active material.